Epigallocatechin-3-O-gallate derivatives represented by the following general formula (I):
[wherein R1 through R6 are each a hydrogen atom or a methyl group and at least one of R1 through R6 is a methyl group], epicatechin-3-O-gallate derivatives represented by the following general formula (II):
[wherein R1 through R5 are as defined above and at least one of R1 through R5 is a methyl group] and isomers thereof are naturally occurring compounds that serve as effective antiallergic agents. These compounds are obtained by methylation of epigallocatechin-3-O-gallate represented by the following chemical formula (III):
epicatechin-3-O-gallate represented by the following chemical formula (IV):
or isomers thereof (Patent Document 1 and Non-Patent Document 1).
The number of allergy patients is rapidly increasing due to changes in the living environment in recent years. The treatment of allergic diseases generally takes a long time and patients are strongly recommended to eat food products that do not cause side effects and can be safely eaten everyday in order to alleviate these diseases. Thus, there is a great need for such food products. Epigallocatechin-3-O-gallate (which may be referred to simply as “EGCG,” hereinafter) is a major component present in tea that is known to have antiallergic activity (Non-Patent Document 2). The compound has a structure represented by the following chemical formula (V):

Recent studies have revealed that epigallocatechin-3-O-(3-O-methyl)gallate, epicatechin-3-O-(3-O-methyl)gallate and the like have even higher antiallergic activity (Patent Document 1, Non-Patent Document 1).
Yabukita, one of the most common cultivars of tea, is known to contain significant amounts of EGCG but no methylated catechins such as epigallocatechin-3-O-(3-O-methyl)gallate and epicatechin-3-O-(3-O-methyl)gallate. While some tea cultivars, including Seishin dai-pan, Benihomare, Benifuji and Benifuki, contain abundant methylated catechins, most of them are rare and difficult to obtain. Thus, a way is needed to convert readily available EGCG into more valuable methylated catechins.
Although several processes for methylating EGCG have been proposed in Non-Patent Document 3, Patent Document 2 and Patent Document 3, each relies upon chemical synthesis or modification and can hardly be used to specifically methylate the hydroxyl groups at positions 3, 4 and 5 of the galloyl group, as represented by the following formula:

Besides, it is desirable to avoid the use of chemically synthesized compounds in food products. For these reasons, enzymes are needed that can effectively synthesize methylated catechins in a site specific manner.    [Patent Document 1] Japanese Patent Laid-Open Publication No. 2000-159670    [Patent Document 2] Japanese Patent Laid-Open Publication No. Sho 61-145177    [Patent Document 3] Japanese Patent Laid-Open Publication No. 2002-255810    [Non-Patent Document 1] Sano M, Suzuki M, Miyase T, Yoshino K, Maeda-Yamamoto M: J. Agric. Food Chem. 47(5) (1999): 1906-1910    [Non-Patent Document 2] Matsuo, N. et al., Allergy 52 (1997): 58-64    [Non-Patent Document 3] J. Biochem. 55 (1964): 205